Most of Grass Land is composed of a vast, grass-grown plain with a dirt track leading all the way through it. Some large, cyan-colored hills can be seen in the background, along with trees of varying heights. The level is largely populated by green Koopa Paratroopas and Paragoombas. At one point in the level, Mario and Yoshi are also attacked by a covey of Bullet Bills. Somewhere near the end of the level, the player reaches a large circular place on the way. A Hammer Bro attacks the heroes here, and he has to be fought off in order for Mario and Yoshi to continue on their journey. The level also features a lake at one point which has to be jumped over.

At the end of the Grass Land level, the player battles Lemmy Koopa. The Koopaling fights Mario and Yoshi in a large bipedal robot modeled after his own image, with the robot's torso looking like his head. He attacks by firing green blasts out of one of the four cannons on the robot's two arms. Occasionally, he stops attacking and just leaps around from side to side. If taken enough damage, the head of the robot will come off and reveal Lemmy Koopa, sitting in a contraption that resembles his father's Koopa Clown Car. At this point, he can be attacked directly. After another few attacks from Mario's Super Scope, Lemmy Koopa gets launched into the sky, holding a white flag, and the level will be completed after Mario receives the gem the boss dropped.